GB948025A - Improvements in or relating to relaxation generators of the free running type - Google Patents

Abstract

948,025. Transistor pulse circuits. PHILIPS ELECTRICAL INDUSTRIES Ltd. May 31, 1961 [June 3, 1960], No. 19651/61. Heading H3T. In a relaxation oscillator, a transistor is biased into the conductive state and the positive feedback path between the control electrode and the relaxation capacitor is closed via a diode, normally rendered non-conductive by the bias on the control electrode. As shown, a transistor 1 has positive feedback via transformer 2 and diode 9. In the absence of pulses at point 24, the relaxation capacitor 3 charges negatively via resistors 21, 23 until the voltage developed at the junction of resistors 7, 8 is reached, when diode 9 becomes conductive, closing the positive feedback path so that the circuit executes a half-cycle of oscillation. Capacitor 3 is discharged via the transistor 1 and the diode 9, whereupon the diode becomes biased off until the capacitor C is recharged again. The base current is limited by resistor 10 and diverted via diode 11 when excessive. The transistor characteristics have less effect on the operation than in a conventional blocking oscillator and the diode 9 prevents base leakage current interferring with the charging of capacitor 3. Fig. 1 (not shown) relates to a free-running oscillator as described. Detecting failure of pulses.-Pulses to be supervised are fed to terminal 24, each pulse rendering transistor 15 conductive and discharging capacitor 3 before it reaches the voltage required to cause transistor 1 to oscillate. If the pulses at 24 should fail, transistor 1 begins to oscillate and energizes relay 25 which is latched by unspecified means and operates an alarm 27. A plurality of pulse generators, each connected to individual circuits 29 may be supervised by a single oscillator of the type shown.